264 POMOLOGY 



less every year. All those which kill back more or less regu- 

 larly are native to regions having a longer growing season 

 than that at Ottawa and hence they mature too late there 

 and the wood is not thoroughly ripened. He, therefore, con- 

 cludes that a tree or shrub which will withstand a test win- 

 ter at Ottawa must ripen its wood early. ^ Not only do the 

 more mature trees exhibit greater hardiness, but they also 

 become more hardy as the winter advances until they again 

 respond to growing conditions as spring approaches. While 

 writers have connnonly assigned the reason for lack of hardi- 

 ness to a higher moisture-content of the tissue, Chandler 

 has shown that, with the exception of the cambium, the tis- 

 sue contains as much moisture later in the winter when it is 

 more hardy as when it enters the dormant period. "It 

 would seem highly probable that, except in the case of cam- 

 bium, the additional hardiness acquired by the different 

 tissues of the tree as they pass into Avinter, is due to a change 

 in the protoplasm such that it can withstand the great loss 

 of water rather than a change in the percentage of moisture 

 or in sap concentration. It is also possible that changes in 

 the sap solute that lower its eutectic point may occur and 

 that these may increase the resistance to cold by holding 

 water unfrozen to protect the protoplasm from too com- 

 plete desiccation at lower temperatures." 



An additional point of evidence that maturity and growth 

 conditions the previous season affect the resistance of trees 

 to cold, is the observation that trees having their foliage 

 injured or destroyed by insects or spray burning suffer seri- 

 ous killing of the wood. Also the inner surface of branches 

 which possess less foliage is nearly always more tender than 

 the exposed sides. ^ 



1 Proc. Amer. Soc. Hort. Sci. 1912. p. 59. 



2 Proc. Amer. Soc. Hort. Soc. 15th Rept. 1918. p. 18. Card, F. W. 

 Bush-Fruits. Macmillan Co., Rev. Ed., 1917. p. 56. 



